Specify Android SDK Platform in plugin configuration

Fixes the following deployment error:

    [ERROR] Failed to execute goal com.jayway.maven.plugins.android.generation2:android-maven-plugin:3.5.4-SNAPSHOT:generate-sources (default-generate-sources) on project compatibility-v7-gridlayout: Execution default-generate-sources of goal com.jayway.maven.plugins.android.generation2:android-maven-plugin:3.5.4-SNAPSHOT:generate-sources failed:  No Android Platform Version/API Level has been configured.  Add e.g. <sdk><platform>17</platform></sdk> to the plugin configuration. -> [Help 1]
    org.apache.maven.lifecycle.LifecycleExecutionException: Failed to execute goal com.jayway.maven.plugins.android.generation2:android-maven-plugin:3.5.4-SNAPSHOT:generate-sources (default-generate-sources) on project compatibility-v7-gridlayout: Execution default-generate-sources of goal com.jayway.maven.plugins.android.generation2:android-maven-plugin:3.5.4-SNAPSHOT:generate-sources failed:  No Android Platform Version/API Level has been configured.  Add e.g. <sdk><platform>17</platform></sdk> to the plugin configuration.
	at org.apache.maven.lifecycle.internal.MojoExecutor.execute(MojoExecutor.java:225)
	at org.apache.maven.lifecycle.internal.MojoExecutor.execute(MojoExecutor.java:153)
	at org.apache.maven.lifecycle.internal.MojoExecutor.execute(MojoExecutor.java:145)
	at org.apache.maven.lifecycle.internal.LifecycleModuleBuilder.buildProject(LifecycleModuleBuilder.java:84)
	at org.apache.maven.lifecycle.internal.LifecycleModuleBuilder.buildProject(LifecycleModuleBuilder.java:59)
	at org.apache.maven.lifecycle.internal.LifecycleStarter.singleThreadedBuild(LifecycleStarter.java:183)
	at org.apache.maven.lifecycle.internal.LifecycleStarter.execute(LifecycleStarter.java:161)
	at org.apache.maven.DefaultMaven.doExecute(DefaultMaven.java:319)
	at org.apache.maven.DefaultMaven.execute(DefaultMaven.java:156)
	at org.apache.maven.cli.MavenCli.execute(MavenCli.java:537)
	at org.apache.maven.cli.MavenCli.doMain(MavenCli.java:196)
	at org.apache.maven.cli.MavenCli.main(MavenCli.java:141)
	at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
	at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:39)
	at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:25)
	at java.lang.reflect.Method.invoke(Method.java:597)
	at org.codehaus.plexus.classworlds.launcher.Launcher.launchEnhanced(Launcher.java:290)
	at org.codehaus.plexus.classworlds.launcher.Launcher.launch(Launcher.java:230)
	at org.codehaus.plexus.classworlds.launcher.Launcher.mainWithExitCode(Launcher.java:409)
	at org.codehaus.plexus.classworlds.launcher.Launcher.main(Launcher.java:352)
    Caused by: org.apache.maven.plugin.PluginExecutionException: Execution default-generate-sources of goal com.jayway.maven.plugins.android.generation2:android-maven-plugin:3.5.4-SNAPSHOT:generate-sources failed:  No Android Platform Version/API Level has been configured.  Add e.g. <sdk><platform>17</platform></sdk> to the plugin configuration.
	at org.apache.maven.plugin.DefaultBuildPluginManager.executeMojo(DefaultBuildPluginManager.java:110)
	at org.apache.maven.lifecycle.internal.MojoExecutor.execute(MojoExecutor.java:209)
	... 19 more
    Caused by: com.jayway.maven.plugins.android.InvalidConfigurationException:  No Android Platform Version/API Level has been configured.  Add e.g. <sdk><platform>17</platform></sdk> to the plugin configuration.
	at com.jayway.maven.plugins.android.AndroidSdk.<init>(AndroidSdk.java:85)
	at com.jayway.maven.plugins.android.AbstractAndroidMojo.getAndroidSdk(AbstractAndroidMojo.java:1150)
	at com.jayway.maven.plugins.android.phase01generatesources.GenerateSourcesMojo.generateR(GenerateSourcesMojo.java:459)
	at com.jayway.maven.plugins.android.phase01generatesources.GenerateSourcesMojo.execute(GenerateSourcesMojo.java:193)
	at org.apache.maven.plugin.DefaultBuildPluginManager.executeMojo(DefaultBuildPluginManager.java:101)
	... 20 more